switch
(PHP 4, PHP 5, PHP 7, PHP 8)
The switch statement is similar to a series of
IF statements on the same expression. In many occasions, you may
want to compare the same variable (or expression) with many
different values, and execute a different piece of code depending
on which value it equals to. This is exactly what the
switch statement is for.
Note: Note that unlike some other languages, the continue statement applies to
switchand acts similar tobreak. If you have aswitchinside a loop and wish to continue to the next iteration of the outer loop, usecontinue 2.
Note:
Note that switch/case does loose comparison.
In the following example, each code block is equivalent.
One uses a series of if and
elseif statements, and the other a
switch statement. In each case, the output is the same.
Example #1 switch structure
<?php
// This switch statement:
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
}
// Is equivalent to:
if ($i == 0) {
echo "i equals 0";
} elseif ($i == 1) {
echo "i equals 1";
} elseif ($i == 2) {
echo "i equals 2";
}
?>
It is important to understand how the switch
statement is executed in order to avoid mistakes. The
switch statement executes line by line
(actually, statement by statement). In the beginning, no code is
executed. Only when a case statement is found
whose expression evaluates to a value that matches the value of the
switch expression does PHP begin to execute the
statements. PHP continues to execute the statements until the end
of the switch block, or the first time it sees
a break statement. If you don't write a
break statement at the end of a case's
statement list, PHP will go on executing the statements of the
following case. For example:
<?php
switch ($i) {
case 0:
echo "i equals 0";
case 1:
echo "i equals 1";
case 2:
echo "i equals 2";
}
?>
Here, if $i is equal to 0, PHP would execute all of the echo
statements! If $i is equal to 1, PHP would execute the last two
echo statements. You would get the expected behavior ('i equals 2'
would be displayed) only if $i is equal to 2. Thus,
it is important not to forget break statements
(even though you may want to avoid supplying them on purpose under
certain circumstances).
In a switch statement, the condition is
evaluated only once and the result is compared to each
case statement. In an elseif
statement, the condition is evaluated again. If your condition is
more complicated than a simple compare and/or is in a tight loop,
a switch may be faster.
The statement list for a case can also be empty, which simply passes control into the statement list for the next case.
<?php
switch ($i) {
case 0:
case 1:
case 2:
echo "i is less than 3 but not negative";
break;
case 3:
echo "i is 3";
}
?>
A special case is the default case. This case matches
anything that wasn't matched by the other cases. For example:
<?php
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
default:
echo "i is not equal to 0, 1 or 2";
}
?>
Note: Multiple default cases will raise a
E_COMPILE_ERRORerror.
Note: Technically the
defaultcase may be listed in any order. It will only be used if no other case matches. However, by convention it is best to place it at the end as the last branch.
If no case branch matches, and there is no default
branch, then no code will be executed, just as if no if statement was true.
A case value may be given as an expression. However, that expression will be evaluated on its own and then loosely compared with the switch value. That means it cannot be used for complex evaluations of the switch value. For example:
<?php
$target = 1;
$start = 3;
switch ($target) {
case $start - 1:
print "A";
break;
case $start - 2:
print "B";
break;
case $start - 3:
print "C";
break;
case $start - 4:
print "D";
break;
}
// Prints "B"
?>
For more complex comparisons, the value true may be used as the switch value.
Or, alternatively, if-else blocks instead of switch.
<?php
$offset = 1;
$start = 3;
switch (true) {
case $start - $offset === 1:
print "A";
break;
case $start - $offset === 2:
print "B";
break;
case $start - $offset === 3:
print "C";
break;
case $start - $offset === 4:
print "D";
break;
}
// Prints "B"
?>
The alternative syntax for control structures is supported with switches. For more information, see Alternative syntax for control structures.
<?php
switch ($i):
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
default:
echo "i is not equal to 0, 1 or 2";
endswitch;
?>
It's possible to use a semicolon instead of a colon after a case like:
<?php
switch($beer)
{
case 'tuborg';
case 'carlsberg';
case 'stella';
case 'heineken';
echo 'Good choice';
break;
default;
echo 'Please make a new selection...';
break;
}
?>
